PSALTER - 1. The Psalter is the book of David, the King and Prophet. It is so termed because the majority of the psalms in it were written by the holy Prophet David. In these psalms, the holy Prophet opens his soul to God, with grief in repenting for the sins he has committed, and with joy in glorifying the endless perfection of God. He expresses gratitude for all the mercies of His care; he seeks help amidst all the obstacles that confront him. For this reason the Psalter is used more than any other service book during the course of the services.
2. For liturgical use the Psalter is divided into twenty sections called kathismata (derived from the Greek word "to sit," as it is customary to sit while they are being read) with certain prayers following each section.